What is the definition of "older?" If the unit is 10-12 years old or less, it's probably 50:1. Older than that, it may be 32:1 Call Partner, give them the SN and see what they say.

I was working in the small engine industry when 50:1 ratios first came out, as a result of much better formulated and synthetic blends. Many were skeptical about mixing 2 ounces of oil with one gallon of gas....I remember landscaper after landscaper coming into the shop and buying three bottles for one gallon of gas, and then they wondered why their units were all smoking like a crop duster and fouling plugs. And then the world almost came to an end when Lawn Boy issued a factory statement that yes, they approved of running their 32:1 engines on a 50:1 synthetic mix!

It is recommended to mix the oil with 89 octane or higher fuel at a ratio of 50:1 using Husqvarna two cycle mix (Partner Brand Mix oil is the same if it is still available in your area). If you use another well known brand it is recommended to mix at 25:1.

It's fine by me if you choose a different brand oil for each of your tools,save yourself a few headaches and standardize.

A lot of us have done this before.

Actually Husqvarna and Shindaiwa are the same oil....blended and packaged
by Spectrum Corporation in Tennessee.Stihl has few types of 2 cycle oil one
is made by Castrol/BP lubricants in Maryland,another in Germany,and a couple
are blended in the U.S. by Omni Specialty Packaging in Louisiana.

Manufacturers always "recommend" their own brand.

I don't use Mopar oil in my Dodge,and my wife doesn't use Motorcraft oil in her Ford.